There are numerous industrial and other processes that produce waste heat, particularly waste heat that is or can be converted to a heat source in the approximate range of 34° F. to 210° F. Heat in these low grade thermal ranges may also be obtained from geothermal sources, including man-made geothermal sources such as those occurring in abandoned oil and natural gas wells, as well as natural water bodies (oceans, lakes, rivers), solar and wind sources. Heat in this range is difficult to utilize since it is too low to be used in conventional Rankin cycle or other vapor cycles to generate useful energy. Accordingly, there is a need for a more efficient method of extracting useful work and electricity from heat, and particularly from heat from low grade thermal sources.